Do you use cold cathodes in you case? The boys at CaseModGod.com have an interesting article for every enthusiast to read, pretty
scary!

I smell smoke... my buddy MARKLAR went through it twice before it finally happened to me, I heard a really loud "POP!" and then caught a whiff of smoke when powering on a just completed modded system. After my initial reaction of "What the hell?!?" I saw that the inverter lay in three pieces on the bottom of the case... not good. You can see in the picture below what appears to be a capacitor that now more closely resembles a piece of fluffy, flammable popcorn.